One thing to check is the adjustment of the accelerator pump linkage. It could be juicing the carb. at idle if its set up too tight. My Holley is different but the instructions call to check it WOT with a feeler gage. For starters make sure its not engaged at all at idle condition.

Vacuum line's need to be hooked up to set idle. Check that your linkage has enough travel, secondary's are closing all the way, that the spacer and gaskets are not interfering with the throttle plates, and that the spacer and gaskets are fully sealing the base of the carb which if they are not would cause a vacuum leak and high idle.

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If you leave the vacuum advance line off especially when using manifold vacuum for the advance it will raise the idle by several hundred rpm's when it is reconnected. Only time to disconnect the vacuum advance line is when setting initial timing.

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It used to be, God bless America, it has become God help America